1. Field of the Invention
This invention relates to drawn polyester yarn of enhanced strength and improved adhesion properties which is used for reinforcing elastic structures such as tires, conveyor belts and the like.
2. Description of Related Art
Elastic structures such as tires, conveyor belts and the like have long been reinforced using yarns made of a wide variety of materials. Initially, the reinforcements used were made of rayon and polyamide, but over time polyester fiber became more and more important, too. To improve the suitability of polyester fiber for use as reinforcing material, both the fiber itself and the adhesive material have been further developed. For instance, the hydrolysis resistance of polyethylene terepthalate has been improved by increasing the molecular weight and reducing the carboxyl end group content. Yarn strength improved as spinning and drawing technology improved.
The adhesion between the yarn material and the elastic material such as rubber, Caoutchouc, etc. improved as the result of the development of a whole series of dip systems. Many known adhesives are based on epoxy compounds, as described for example in U.S. Pat. No. 3,793,425 and in U.S. Pat. No. 4,044,189. U.S. Pat. No. 4,438,178, for example, teaches ethers or esters based on epichlorohydrin and polyhydric alcohols or polycarboxylic acids. These compounds again contain epoxy groups.
Adhesives without epoxy groups are a recent development. For instance, EP-A1-0 637 602 discloses organic compounds containing 2-halomethyloxyethylene units, secondary hydroxyl groups, and ester groups derived from organic acids. These compounds are essentially free of halohydrin and epoxy groups and are used, for example, for improving the adhesion of fibers composed of polyamides, polyester, carbon, etc.
EP-A2-0 395 432, finally, describes polyesters which contain at least one 2-halomethyloxyethylene unit and a 2,3-dihydroxypropyl end group and which are likewise essentially free of epoxy groups and halohydrin groups. The aforementioned compounds which are free of epoxy and halohydrin groups are applied to the fibers to be treated as aqueous emulsions or aqueous solutions having a considerable water content.
Japanese Kokai 7-70819 describes a process for drawing undrawn polyester yarn spun at high speed wherein the yarn is taken off and treated before drawing with an oily fiber finish having a water content of not more than 10%. The yarn is then subjected to multistage drawing at different temperatures. The yarn thus produced can be used, for example, in the form of a cord for reinforcing rubber articles.
This Japanese patent application does not teach the improved adherence to rubber, and the strengths obtained are below those achieved according to the present invention. Nor does said reference motivate one skilled in the art in any way to use compounds as improved adhesives, as is the case with the present invention.